Presented with an accounting fact – that, on Shell's terms, wind power is deemed insufficiently profitable – observers are expected to automatically understand their logic, nod in agreement and move on.

And they have, of course, been able to "make the numbers work" for heavily polluting tar sands. The high and fluctuating price of oil has gifted Shell massive, windfall profits from an asset which could be seen as a common global inheritance, one whose use carries an equally high cost. What makes the need for one set of numbers to "work" trump all other considerations, even the ultimate one of a climate fit for civilisation? How did we get to the odd state of affairs where a company citing extreme and narrow self-interest, can make investment decisions with profound negative decisions for the rest of society, while expecting and receiving impunity? With George Osborne as chancellor, they even get an understanding, indulgent pat on the shoulder to accompany the new tax breaks given to the oil sector in the budget.

Take one small step away from the detached, insulated and self-reinforcing cultural sphere of elite business and the situation quickly appears deeply strange. Global energy companies like Shell are few and massive. The process of rapidly liquidating humanity's once-off fossil fuel inheritance is both eye-wateringly profitable, nicely protected, and cushioned by public infrastructure investment and the afore-mentioned tax breaks. Even though they are private companies, at one level the operations of players like Shell and BP are elaborately interwoven with the workings of governments (wars being fought and governments changed with their interests in mind) and frequently collude on issues of national energy security. They are not fully separate entities.

A quid pro quo must be an acknowledgement that their vast influence over our present and future energy choices – and hence our very futures - carries particular responsibilities to do the right thing by all of us. The argument against some kind of public interest oversight of key decisions by agents like Shell - that it's a private company, spending its own money in a free market, doesn't wash. Shell, it should be noted in passing, have been found guilty more than once by the Advertising Standards Authority for exaggerating their green credentials.

So, to what could we compare their glib, yet profound, invoking of the numbers not working? What if you took your child to a hospital's paediatric ward only to find it closed, the hospital management having opened a bar instead because it earned them more money? Or what about a tobacco company whose marketing currently promotes smoking (and therefore an early death) among young women in Asia, being given the chance to shift out of producing cigarettes, and into growing fairly traded fruit instead, but which opts to stay with tobacco because the margins are better? How is tobacco marketing different to slow, coerced suicide?

Both are circumstances in which socially unacceptable decisions are made in which the only ultimate justification is profit maximisation. Both could be accused of being unlikely and unreal (but are they?). Neither, however, touches the potential global consequence of Shell's choice.

Capitalism can be thought of as a system in which the returns to capital take priority over other concerns. Yet questioning capitalism, or suggesting its days may be numbered, raises fairly universal disbelief or derision. Even intelligent members of the political left struggle to imagine a different economic system, most suggesting only reforms to business as usual.

Yet Shell's throwaway remark about numbers not working reveals a profound truth of capitalism: when pushed to choose between profit and survival, it chooses profit irrespective of collective consequence. There, with refreshing clarity in that simple statement, is why the legal structures that privilege finance and underpin capitalism cannot continue, and why, regardless of what benefits it may have brought to a wealthy global minority in the past, capitalism can not be the operating system of a global economy already transgressing environmental limits. Some argue that we merely need to wait for the price signal to reorient us toward environmentally safe choices.

But that change needs to happen now as the International Energy Agency and many others repeatedly point out (in fact, because of the time lag between carbon emissions and their consequences in global warming it needed to happen decades ago).

And, as the Shell decision makes clear with rare, flat simplicity, there is no price signal currently levering the necessary change to happen within the unavoidable time frame for action. Oddly, a company whose business model is based on the exploitation of irreplaceable natural assets for profit, and which epitomises the privilege of finance under capitalism, may just have provided the most convincing example of why the economic system it flourishes under must be replaced.